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...energy factories called mitochondria, in addition to the cell's DNA - packaged into twenty three chromosomes. At the tip of the sperm's head is a package that contains enzymes that break down protective layers on the egg's surface. Not all human sperm cells look the same. Some have two heads or no heads, some have huge heads, some have small tails or no tails, others may...

...energy for life. However, we cannot digest all of the food we eat and what remains undigested, ends up in the sewage system. About 10 billion litres of sewage are produced every day in England and Wales and this has to be treated to remove harmful substances and pathogenic microbes before the waste can be safely released into the environment. The main component of sewage...

...energy, are transported via other organisms (e.g. hosts) or environmental processes (e.g. flowing water). It is possible some transported species (i.e. ‘alien’ to their new environment) will survive and colonise their new destination, unless limited by environmental factors or antagonistic organisms. When such introduced ‘alien’ species start to infest and...